Lecture 11

Networks I: Telephone or Circuit Switched Networks

April 21, 2004



Introduction:  

Networking is a hugh subject and we have but two or three lectures to attempt to say something meaningful.  From the user's point of view the key issues are network protocols and architectures.  These are subjects covered in detail in courses like CSCI E-131ab, CSCI E-132 and CSCI E-135, for example.  In this course we have tried to emphasize the physical factors governing the evolution of communication systems and in this context we will limit our discussion to aspects of networking where the impact of optical signaling is profound.

Why do we need networks?  

Answer: The "n squared" problem of point-to-point, fully connected communication (discussion)

Network topologies reference

Star networks: hierarchical or centralized networks (discussion)

Bus and ring networks: distributed control networks (discussion)

Trunking  (discussion)

Hierarchy of analog telephone networks reference

Lower levels of analog telephone hierarchy (source)
FDM analog hierarchy (source)
Pre-divestiture telephone hierarchy (source)
Post-divestiture telephone hierarchy (source)
Post-Telcom 95 telephone hierarchy I (source)
Post-Telcom 95 telephone hierarchy II (source)

Traffic:

From lecture notes of Professor Luiz A. DaSilva:

Switching: reference

Switching Modalities: (discussion)

Switching Functions:

Concentration -- many lines funneled into a few trunks
Distribution or Routing -- interconnecting trunk lines
Expansion -- a few trunks expanded to many lines

Manual Telephone Switching:

Manual

Automatic Telephone Switching:

Strowger Switches

Matrix or Crossbar Switches
Clos's rule for non-blocking networks

Electronic Switching :

Signaling System 7 (SS7) is a global standard for telecommunications that defines the procedures and protocol by which network elements in the public switched telephone network (PSTN) exchange information over a digital signaling network to effect wireless (cellular) and wireline call setup, routing and control.
TEKELEC has very complete discussion of SS7 at The Signaling System 7 Information Center.  Requires registration to access.

Other references:
From Performance Technologies the SS7 Tutorial.
From Webopedia SS7 Definitions.
From TechFest the SS7 Overview.
From Intel the Public Network Signalling Tutorial.

General References:

David Massey's Telephone Tribute is an incredible resource covering many aspects of telephone history and technology.

Vermont Telecom Advancement Center

Humber College's The Public Switching Telephone Network (PSTN)

Public Switched Telephone Network (S-PSTN)

NTT's How Telephones Connects

AT&T Long Lines Technology and Equipment

Switching and Signaling

  

This page was prepared and is maintained by R. Victor Jones
Comments to: jones@deas.harvard.edu.

Last updated April 27, 2004